Chances are good that your DPFE sensor has gone belly up. The 2001~2002 DPFE's are not reliable. It is not for sure the DPFE, but the odds are definitely in its favor. Replacement cost is about $40~60 and it's easy to install.
Take it to the dealer, it is under an extended warranty. I got a letter from Ford about 2 years ago, and just had mine replaced about a month ago. I beleive the warranty pushes it out to 5 years or 80k miles. In any case, mine was free at 58k miles.